JPS6256564B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switching circuit for a magnetic recording/reproducing device.
In particular, the purpose is to electronically and rationally switch the recording/reproducing head in the recording/reproducing switching circuit.

A conventional switching circuit will be explained by taking the recording and reproducing circuit shown in FIG. 1 as an example. In the figure, 1, 2
is a magnetic head for both left and right channel recording and playback,
3 and 4 are left and right channel playback amplifiers, 5 and 6 are left and right channel recording amplifiers, 7 and 8 are recording and playback selector switches, and the switches 7 and 8 are shown switched to the playback position in the figure. There is. 9,1
0 is an adjustment capacitor for supplying AC bias to the magnetic heads 1 and 2, 11 and 12 are trap circuits to prevent AC bias from leaking to the recording amplifiers 5 and 6, and 13 is an AC bias oscillation circuit. The trap circuits 11 and 12 are composed of parallel circuits of coils and capacitors, and by tuning their resonance frequency to the oscillation frequency of the bias oscillation circuit 13, leakage of AC bias to the recording amplifiers 5 and 6 is minimized. .

In this conventional switching circuit, during reproduction, the reproduction signal from the magnetic heads 1 and 2 is transmitted to the magnetic heads 1 and 2.
One terminal is the contact 7 of the recording/playback switch 7.
a, 7b, contact 8a of recording/playback switch 8,
Since the signal is grounded through 8b and the other terminal is connected to the reproduction amplifiers 3 and 4, it is amplified by the reproduction amplifiers 3 and 4. At this time, since the outputs of the recording amplifiers 5 and 6 and the bias oscillation circuit 13 are grounded by the recording and playback switches 7 and 8, they do not interfere with the playback signal. (The bias oscillation circuit 13 is made not to oscillate in most cases during playback.) On the other hand, to put the device into the recording state, turn the recording/playback switch 7 into contacts 7a to 7c, and turn the recording/playback switch 8 into contacts 8a to 8c. Switch to Then, the playback amplifiers 3 and 4 of the recording and playback heads 1 and 2
The terminal connected to the input side of is grounded and the output of the recording amplifiers 5 and 6 and the bias oscillation circuit 13
Since the output of the recording amplifiers 5 and 6 is separated from the ground, an AC bias current flows through the adjustment capacitors 10 and 9 to the recording and playback heads 1 and 2, and the output currents of the recording amplifiers 5 and 6 also flow superimposed on the AC bias.
You will be able to record.

As described above, the conventional switching circuit uses a mechanical switch to change the connection of the recording/reproducing head, which has caused the following problems. Firstly, it requires a large amount of force to switch between recording and playback, secondly it is difficult to time the switchover properly, and thirdly it has a short lifespan.

Regarding the first problem, using a plunger or the like to switch the recording/playback switch reduces the force required for the user's operation, but the sound when switching the plunger is loud and the amount of power required to drive the plunger is large. New problems arise, such as the need for The second switching timing issue is related to the fall and rise of the bias oscillation output, but if the bias current is suddenly cut off at the recording/playback switching head while the bias current is flowing to the recording/playback head, the head is magnetized and causes noise, but it is difficult to get the timing right. Regarding the third point of life, since the recording/playback changeover switch is a mechanical changeover switch, it has a shorter lifespan and is more likely to break down than an electronic changeover.

The present invention eliminates such conventional drawbacks, and one embodiment thereof will be described below with reference to FIGS. 2 and 3. In FIG. 2, parts having the same functions as those in FIG. 1 are given the same numbers, and detailed explanations are omitted. 14, 15, 1 in Figure 2
6 is a transistor that becomes conductive during playback and non-conductive during recording; these transistors 1
4-16 are driven by transistor 17. Transistors 18 and 19 are non-conductive during playback and conductive during recording;
0 is a power supply, 21 is a recording/playback switching command input terminal, and when a voltage exceeding a certain value determined by the division ratio of resistors 22 and 23 and the voltage of the power supply 20 is applied to this input terminal 21, the transistor 17 becomes non-conducting. becomes. 24 to 29 are resistors, and 30 is a diode.

In the above embodiment, when the circuit is put into a reproducing state, the input terminal 21 is first grounded. In this way, a base current flows through the transistor 17 via the resistor 23, and the transistor 17 becomes conductive. Therefore, since the base current flows to the transistors 14, 15, 16 via the transistor 17 and the resistors 24, 25, 26, the transistors 14, 15, 16
16 becomes conductive, and bias supply side terminals 31 and 34 of heads 1 and 2 are grounded via transistors 14 and 16 and transistors 15 and 16, respectively. On the other hand, the base sides of the transistors 18 and 19 are grounded through the isolation diode 30, and since the forward voltage of this diode 30 is lower than the forward voltage of the transistors 18 and 19, they do not conduct. Terminals 33 and 32 are disconnected from the ground, and reproduction outputs from heads 1 and 2 are input to reproduction amplifiers 3 and 4.

Next, in order to change from the playback state to the recording state, a voltage higher than a certain value determined by the division ratio of the resistors 22 and 23 and the voltage of the power supply 20 is applied to the input terminal 21 as described above to turn the transistor 17 off. do. At the same time, the base currents of the transistors 14, 15, and 16 cease to flow and become non-conductive, so that the bias supply terminals 31 and 34 of the heads 1 and 2 are disconnected from the ground. On the other hand transistor 1
A base current flows from the power supply 20 to the transistors 8 and 19 via the resistors 27 and 28, and the transistors 18 and 19 become conductive, and the other terminals 33 and 3 of the head
2 is grounded.

Therefore, the AC bias is applied from the bias oscillator circuit 13 to the heads 1 and 10 via the adjustment capacitors 9 and 10.
The recording signals from the recording amplifiers 5 and 6 also flow to the heads 1 and 2 via the bias trap circuits 11 and 12, and are superimposed on the AC bias and are recorded.

In this recording state, the voltage of the bias supply terminals 31 and 34 of the head with respect to ground is very high. Therefore, in the circuit of this embodiment shown in FIG. 2, the combination of transistors is used to prevent the peak value of the AC bias from exceeding the reverse breakdown voltage of the transistors.
That is, in Fig. 3, 14, 15, 16, 17
is a model when transistors 14 to 17 are non-conducting. Further, 35 and 36 represent the voltages of the bias supply terminals 31 and 34 of the heads 1 and 2.

In FIG. 3, transistors 14, 15, 1
To explain the state in which the reverse breakdown voltage of 6 and 17 is not exceeded, 3
5 and 36 AC bias voltages are applied to terminal 3, respectively.
When 1 and 34 become positive with respect to the ground, it is blocked by the reverse withstand voltage of diodes 14a and 15a, and when the AC bias is reversed and a reverse voltage is applied, diode 1
Since the reverse breakdown voltage of 6b and 17a is used to block the voltage, the bias oscillation voltage causes the transistors 14,
The bias waveform will not be distorted due to conduction between 15 and 16, and the same result as when disconnected from the ground by a mechanical switch can be obtained. As described above, according to the switching circuit of this embodiment, by applying an input of H level or L level to the input terminal 21, it is possible to easily switch between recording and reproduction of the recording/reproducing heads 1 and 2.

A series circuit of transistors 14 and 15 is connected between the terminal 31 of head 1 and the terminal 34 of head 2 constituting the stereo.
Since the transistor 16 is connected between the mutual connection point and the ground, and the transistors 14, 15, and 16 are made conductive and non-conductive at the same time, the transistors 14 and 15 inserted for the left and right channels are connected to a common Since the transistor 16 can be connected to the ground, the circuit can be easily configured, and the number of parts can be reduced, resulting in lower cost.

The signal to be applied to the input terminal 21 can be easily obtained by applying a circuit which normally lights up a display element such as a light emitting diode as an indication of recording or playback.

As explained above, according to the switching circuit of the magnetic recording and reproducing device of the present invention, it is possible to easily electronically switch the recording and reproducing head, thereby achieving a long circuit life, improved reliability, power saving, and less switching noise. The effect is significant.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a switching circuit of a conventional magnetic recording and reproducing device, FIG. 2 is a circuit diagram showing a switching circuit of a magnetic recording and reproducing device according to an embodiment of the present invention, and FIG.
The figure is an equivalent circuit diagram of FIG. 2. 1, 2...Magnetic head for both recording and playback, 14-1
6...Transistor.

Claims (1)

[Claims] 1 A first magnetic head for left channel recording and reproduction, a second magnetic head for right channel recording and reproduction, and a bias trap circuit connected to one terminal of each of the first magnetic head and the second magnetic head. The connected left channel recording amplifier, right channel recording amplifier, the first magnetic head, and the second magnetic head.
A left channel reproducing amplifier and a right channel reproducing amplifier connected to the other terminal of each of the magnetic heads, and one terminal of the first magnetic head and one terminal of the second magnetic head are connected in series. A third switching transistor connected between the mutual connection point of the connected first and second switching transistors and the ground, and between the other terminal of the first magnetic head and the second magnetic head and the ground. a control circuit that supplies a signal input to a recording/playback switching command input terminal to the fourth and fifth switching transistors;
When a recording command is input to the recording/playback switching command input terminal, the first to third switching transistors are simultaneously made non-conductive and the fourth and fifth switching transistors are simultaneously made conductive, whereby the first to third switching transistors are made non-conductive and the fourth and fifth switching transistors are simultaneously made conductive. 1. The recording signals from the left channel recording amplifier and the right channel recording amplifier can be recorded on the magnetic tape by the second magnetic head, and when a reproduction command is input to the recording reproduction switching command input terminal, By simultaneously making the first to third switching transistors conductive and simultaneously making the fourth and fifth switching transistors non-conductive, the signals reproduced from the magnetic tape by the first and second magnetic heads are respectively reproduced. A switching circuit for a stereo magnetic recording and reproducing device, characterized in that it is configured to be able to supply a signal to a left channel reproducing amplifier and a right channel reproducing amplifier.